In some hydrocarbon production wells, it is desirable to pump relatively low volumes at significant depths. For example, most gas wells will produce some liquid. If the pressure is inadequate to cause the liquid to flow to the surface along with the gas, the liquid will accumulate at the bottom of the well. The accumulation of liquid can eventually block the flow of gas from the perforations.
Centrifugal pumps are commonly utilized in oil wells for producing high volumes of liquid. A centrifugal pump has a number of stages, each stage having a rotating impeller that cooperates with a diffuser. Typically these pumps are utilized in wells that produce significant amounts of water along with oil. Generally, the number of stages required is proportional to the lift necessary to produce the liquid. For example, a 4″ diameter pump produces about 20 to 25 feet of lift per stage. Consequently, 2500 feet of lift requires 100 or more stages. Such a centrifugal pump would produce far more liquid than would be necessary in most gas wells.
Reciprocating pumps used for low volume oil production typically use a sucker rod extending from the surface to stroke a reciprocating pump in the well. Because of the moving sucker rod, this type of pump is generally not applicable to producing small accumulations of liquid from gas wells. Also, sucker rod pumps are not efficient for pumping low volumes from deep wells because they require a large unit at the surface to accommodate the weight of the sucker rod as well as stretch and compression during each stroke.